1. Field of the Invention
The present invention relates to the production of sodium ferrate by an electrolytic process in a membrane-type electrolysis cell.
2. Description of the Prior Art
Alkali metal and alkaline earth metal ferrates resemble permanganate in having a purple color and, in acid solutions, they evolve oxygen very rapidly.
The prior art teaches two principal methods for making alkali metal and alkaline earth metal ferrates. One method of preparation has been by electrolysis either in unseparated cells or in diaphragm-type electrolytic cells (i.e., multi-chamber cells which have an anolyte separated from the catholyte by a gas-porous, hydraulically permeable separator).
Alkali metal and alkaline earth metal ferrates have also been produced by the reaction of inorganic hypochlorites with iron-containing compounds in aqueous alkaline solutions.
However, sodium ferrate produced by such prior art methods becomes unstable and tends to degrade almost immediately. This lack of stability is due to the hydrolysis of sodium ferrate with water in the cell or the atmosphere to form ferric hydroxide. Also, the prior art methods for making sodium ferrate by electrochemical means also have the problem of anode passivity, which is caused by the formation of ferric oxide film on the iron anode. Further, once formed, this film has been found to catalyze and thus speed up the rate of ferrate decomposition. To prevent such problems, it is necessary to either wash the anode with acid or reverse the current to remove such a ferric oxide film. However, these techniques are costly or time-consuming, or both.
The strong oxidizing properties of ferrates suggest that they may be useful for a variety of commercial uses (e.g., oxidation of chemical moieties in waste water streams). However, the aforesaid instability tends to severely limit such utility for commercial applications. Thus, there is a need at the present time to find a commercial process for producing ferrates.